Heat exchanging tube with spiral groove

ABSTRACT

The present invention relates to a heat transfer tube with spiral groove, comprising a stainless steel tube body with inward convex spiral groove on surface, wherein the stainless steel tube body possesses unequal height and width in the cross sectional view. In the EGR (Exhaust Gas Recirculation) cooling system for automotive engine, such kind of spiral groove tube with the unequal height and width in the cross-section acting as the heat transfer tube for the cooler make the cooler gain higher heat transfer effect, and it is hard to make dirt deposited inside or outside the tube, which greatly improves the emissions performance for automotive engine, and satisfies higher requirement of environmental protection.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority benefit of Chinese patent application No. 200610057223.7 filed on Mar. 9, 2006, the contents of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a heat transfer tube with spiral groove, in particular a heat transfer tube with spiral groove applied in the EGR (Exhaust Gas recirculation) cooling system for automotive engine, and its cross-section has unequal height and width.

DESCRIPTION OF RELATED ART

The EGR cooling technique is an effective and reliable technique to decrease nitrogen oxides (NO_(x)) emissions of diesel engine. The theory is: decreasing the temperature of the exhaust gas by the cooler, and then returning the gas to the engine combustor in order to decrease the temperature of the combustor so as to reduce nitrogen oxides' generation and emissions. Among them, the cooler is the key element in the EGR system, and the heat transfer efficiency thereof decides the temperature of the recirculated exhaust gas. Therefore how to improve the heat transfer efficiency of EGR cooler by guaranteeing economical efficiency is the initial technical index for cooler designing. Moreover, the heat transfer tube is a key element in the cooler, and the thermal efficiency of the cooler is mainly dependent on the heat transfer coefficient of the tube, so it is necessary to improve heat transfer coefficient constantly.

At present, in the EGR cooler of the engine, the most popularly used heat transfer tube adopts a kind of stainless steel tube with internally convex spiral groove on its surface, and the cross section of the tube is circular. However, with the stringent requirement for the automotive pollutant emissions by environmental protection laws and regulations, the heat transfer effect of the tube with spiral groove, which has such kind of circular section, cannot meet the demand in the future that the limit of the nitrogen oxides' generation and emissions of vehicle might be strengthened by several tens or hundred times. For the present more and more stringent emissions requirement and competitive economic market, the heat transfer tube with spiral groove in circular sectional shape cannot meet the need in the engine exhaust recirculation cooling system within limited installation space.

SUMMARY OF THE INVENTION

The present invention aims to provide a heat transfer tube with higher thermal efficiency for improving the situation that the current heat transfer tube with spiral groove in circular sectional shape cannot meet the future requirement for environmental protection in heat transfer efficiency, such tube can greatly improve the thermal efficiency while the volume of the cooler does not vary.

In order to realize the foregoing aim, the present invention provides a heat transfer tube with spiral groove, comprising a stainless steel tube body with inward convex spiral groove on surface, wherein the stainless steel tube body possesses unequal height and width in cross-section view.

In the above-mentioned solution, the sectional shape of said stainless steel tube body can be rectangle, and adjacent two sides are connected by arc transition; the sectional shape of the stainless steel tube body can also be consists of two relative short sides and two relative long sides, wherein the short sides appear as outward convex arcs and the long sides can be straight lines or outward convex arcs; the sectional shape of said stainless steel tube body can also be ellipse. It should be noted that in order to be better described, the sectional shape of said stainless steel tube body presents as the standard shape under the assumption that there is no spiral groove in the tube. The sectional shape of the heat transfer tube in the present invention is the combination of said sectional shape of the stainless steel tube and the sectional shape of said spiral groove. Said spiral groove can be set to be multiple, and each groove can be set continuously or intermitted; the sectional shape of the spiral groove can be “U” shape or “V” shape, which is of benefit to the generation of small size surface; the spiral lift angle β of the groove is designed between 20 and 75 degrees; the depth D of the groove is no less than 0.4^(mm), which can make the full developed turbulence generate in the tube; at the same time, in order to ensure the tube being economical and practical, and to simplify the manufacturing difficulty, all the acute angles of the section are designed to be arc R transition, in which the surface between said groove and said stainless steel tube body is also connected by arc transition so as to make all the surfaces sufficiently exchange heat very well and completely eliminate dead corner during heat exchanging.

When the exhaust gas passes through such kind of heat transfer tube, it can go through the spiral convex part, then the boundary layer of partial wall surface separates and forms vortex backward the spiral convex. Such separation of the boundary layer and generation of vortex make heat transition improved. And the spiral convex can trigger the exhaust gas operate spiral movement, which results in complicated secondary swirl flow (is also called as secondary flow) is generated in the exhaust gas, enlarging the turbulence scale of the exhaust gas, particularly enlarging the disturbance to the boundary layer nearby wall area, accelerating mixing of the fluid in the boundary layer and the core area, which makes heat convection improved; the secondary flow also has the effect to make the sectional speed distribute more even. Especially the design of the flat oval section such as the foregoing four sections like rectangle and ellipse makes the thickness of the boundary layer become thinner greatly by the combined cooperation of the secondary flow and the centrifugal force generated by spiral movement, and meanwhile reduces the critical Renault. In other words, the conversion from laminar flow into turbulence generates ahead of time, and violent turbulence makes dirt severely scoured within the tube. As a result, fouling of the spiral heat transfer tube with such kind of flat oval sectional shape like the foregoing rectangle, ellipse and other two shapes becomes difficult, which is of benefit to heat convection.

In addition, the heat transfer effect of the tube with spiral grooves in circle sectional shape is compared with that of the tube in the above-mentioned flat oval sectional shape by experiment, in which the sectional area is the same. Please see the details in FIG. 1 and FIG. 2. In the drawings, A and B are the curves showing the relationship between the heat transfer coefficient of the tube with spiral groove in flat sectional shape and the cross section area of the tube; A′ and B′ are the curves showing the relationship between the heat transfer coefficient of the tube with spiral groove in flat oval sectional shape and the velocity; C and C′ are respectively the curves showing the relationship between the heat transfer coefficient of the tube with spiral groove in circular sectional shape and the cross section area of the tube, and the relationship between the heat transfer coefficient of the tube with spiral groove in circular sectional shape and the velocity.

As shown in FIG. 1, when the flow areas are the same, comparing with the heat transfer coefficient of the tube with spiral groove in circular sectional shape, the heat transfer coefficient of the tube with spiral groove in flat oval sectional shape is greatly increased.

As shown in FIG. 2, with the increase of the velocity, the heat transfer coefficient of the tube with spiral groove in flat oval sectional shape increases relatively fast, however, the heat transfer coefficient of the tube with spiral groove in circular sectional shape tends to become even rapidly in a certain period.

Therefore, it can be shown that the cooler manufactured according to the present invention can obtain greater cooling effect when the volume keeps the same, which greatly improves the index of automotive gas emissions performance, and satisfies higher requirement of environmental protection.

The technical solution of the present invention will be described in details with reference to the accompanying drawings and the preferred embodiments hereinafter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing the experiment results comparing the relationship between the heat transfer coefficient of the tube with spiral groove in flat oval sectional shape and the cross section area of the tube with the relationship between the heat transfer coefficient of the tube with spiral groove in circular sectional shape and the cross section area of the tube in the present invention;

FIG. 2 is a drawing showing the experiment results comparing the relationship between the heat transfer coefficient of the tube with spiral groove in flat oval sectional shape and the velocity with the relationship between the heat transfer coefficient of the tube with spiral groove in circular sectional shape and the velocity in the present invention;

FIG. 3 is a sketch of the three dimensional drawing of the first embodiment in the present invention;

FIG. 4 is a sketch of the sectional view drawing of the first embodiment shown in FIG. 3;

FIG. 5 is a sketch of the three dimensional drawing of the second embodiment in the present invention;

FIG. 6 is a sketch of the sectional view drawing of the second embodiment shown in FIG. 5;

FIG. 7 is a sketch of the three dimensional drawing of the third embodiment in the present invention;

FIG. 8 is a sketch of the sectional view drawing of the third embodiment shown in FIG. 7;

FIG. 9 is a sketch of the three dimensional drawing of the fourth embodiment in the present invention;

FIG. 10 is a sketch the sectional view drawing of the fourth embodiment shown in FIG. 9.

EMBODIMENTS

FIG. 3 and FIG. 4 are the sketch of the three dimensional drawing and the sectional view drawing of the first embodiment in the present invention respectively. In the drawings, heat transfer tube is a stainless steel tube body 2 with an internally convex spiral groove 21 on its surface. In order to realize the heat exchange with the largest efficiency by using the surface of the heat transfer tube sufficiently, and make it easy to be manufactured, the two adjacent surfaces of the heat tube are set to be connected by arc transition with the radius of R in this embodiment. Removing the sectional shape from the section of said heat transfer tube, the sectional shape of the stainless steel tube body 2 becomes rectangle, wherein the height is not equal to the width, and the adjacent two sides are connected by arc transition, which is shown in FIG. 4, wherein a is the height of the section; the spiral convex can be one or more; the sectional shape of the spiral groove can be set as “U” shape or “V” shape, which is of benefit to the generation of small size surface; the spiral lift angle of the groove is designed between 20 and 75 degrees; the depth D of the groove is no less than 0.4^(mm).

FIG. 5 and FIG. 6 are the sketch of the three dimensional drawing and the sectional view drawing of the second embodiment in the present invention respectively. What differs from the above-mentioned first embodiment is that the two relative short sides of the stainless steel tube body 2 are outward convex arc surfaces with the radius of R1, as shown in FIG. 6; the rest parts are identical to those of the first embodiment. Such setting is easy for manufacturing without decreasing thermal efficiency.

FIG. 7 and FIG. 8 are the sketch of the three dimensional drawing and the sectional view drawing of the third embodiment in the present invention respectively. In order to guarantee the quality of product, basing on the second embodiment, this embodiment also sets the two relative long sides to be outward convex arcs, in other words, the four surfaces of the stainless steel tube body 2 are all set as outward convex arc surfaces, moreover, as shown in FIG. 8, the arc radius R′ of the long side is far longer than the radius R of the short side, so that the phenomenon of surface “sink” will not appear; the rest parts are identical to those of the first embodiment.

FIG. 9 and FIG. 10 are the sketch of the three dimensional drawing and the sectional view drawing of the fourth embodiment in the present invention respectively. This embodiment is an equivalent deformation based on the sectional shape of the above-mentioned third embodiment. That is to say, in the condition of removing the sectional shape of the spiral groove, the sectional shape of the stainless steel tube body 2 is an ellipse, wherein the major axis b is larger than the minor axis of the section; the rest parts are identical to those of the first embodiment.

The cooler manufactured according to the present invention obtains greater cooling effect when the volume keeps the same, which greatly improves the index of automotive gas emissions performance, and satisfies higher requirement of environmental protection.

It will be understood that the above embodiments are used only to explain but not to limit the present invention. In despite of the detailed description of the present invention with referring to above preferred embodiments, it should be understood that various modifications, changes or equivalents can be made by those skilled persons in the field without departing from the spirit and scope of the present invention. 

1. A heat transfer tube with spiral groove, comprising a stainless steel tube body with inward convex spiral groove on surface, characterized in that the stainless steel tube body possesses unequal height and width in cross-sectional view.
 2. The heat transfer tube with spiral groove of claim 1, characterized in that the sectional shape of the stainless steel tube body is rectangle, and adjacent two sides are connected by arc transition.
 3. The heat transfer tube with spiral groove of claim 2, characterized in that the sectional shape of the stainless steel tube body is consist of two relative short sides and two relative long sides, wherein the short sides appear as outward convex arcs and the long sides are straight lines.
 4. The heat transfer tube with spiral groove of claim 3, characterized in that the two relative long sides appear as outward convex arcs.
 5. The heat transfer tube with spiral groove of claim 1, characterized in that the sectional shape of the stainless steel tube body is ellipse.
 6. The heat transfer tube with spiral groove of claim 1, characterized in that the spiral groove is one or multiple.
 7. The heat transfer tube with spiral groove of claim 6, characterized in that the one or multiple spiral groove is set continuously or intermitted.
 8. The heat transfer tube with spiral groove of claim 1, characterized in that the sectional shape of the stainless steel tube body is “U” shape or “V” shape.
 9. The heat transfer tube with spiral groove of claim 8, characterized in that the spiral groove connects to the surface of the stainless steel tube body by arc transition. 